Multiplex speech interpolation system



Feb. R39 QS A. E. MELE-lose:

MULTIPLEX SPEECH INTERPQLATION SYSTEM 9 Shets-Sheel: 1

Filed May 19, 1948 :dan

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Feb. 13, ESSE A. E. MELHoslE MULTIPLEX SPEECH INTERPOLATION SYSTEM Filed May 19, 1948 9 Sheets-Sheet 3 Ffm;

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TALAER C /N/E'A/TO By EELHOSE ATTORNEY FIG. 5 (GAZ'EI) Feb. 13, S A. E. MELHOSE ,9543992 MULTIPLEX SPEECH INTERPOLATION SYSTEM Filed May 19, 1.948 9 Sheets-Sheet 5 I v FVG. 5 6T] WH 7/ 7a GAT/NG PHL SES TAs/ sfeer SIGNAL PCM 576ML Fe. E3, mi A. E.

MULTIPLEX SPEEH INTERPOYLA'ION SYSTEM Filed May 19, 1948 `9 Sheets-Sheet 6 E Rm mw EE MM. E

TTOR/VE V Feb 13 93 A. E..ME| Hosl-:" MSS MULTIPLX SPEECH INTERPOLATION SYSTEM /Nl/EA/rO/Q A. E. MEL HOSE WNW; @.Nml/

Fell 13 1951 A. E. MELHosE 2,541,932

MULTIPLEX SPEECH INTERPOLATION SYSTEM HlMM C.

Patented Feb. 13, 1951 MULTIPLEX SPEECH I NrRPoLA'roN 4SYSTEM Alfred E. Melhose, VWestfield, r`N. J.,A assigner to Bellk Telephone Laboratories,Incorporated, New York, N. Y., a corporation of'NeW York Application May-19, ieiaserfial No. 27,905

1Q Claims. l

This invention relates to multiplex communication, 'and more particularly to the multiplex transmission of telephone calls.

The principal object 'of the invention is to provide for the handling eof calls originating with a number of indep ndent subscribers by ai vlesser number of ltransmission channel `facilities, thus reducing the fraction of the time during `which a transmission "channelI Would otherwise be idle, and'so "enabling economies to be eiiectedfin the provision of transmission apparatus.

,A more Yspec'iilc 'object is to prcvide for the vhandling of the currently active few of Aa number of Aindependent 'and potentially active callers, on 'a time assignment basis.

Astill more specic Vobject is to make Vsuch pro; V'vision for arPulse Code Modulation or other Time Divisin Multiplex Syst In.

A related object is tc make Acommon use tof vcertain 'apparatus compon nts for Time Division Multiplex purposes and Speech Interpolation purpcses.

'These and ether objects lare attained, in" ac'L ccrdtaice with the invention, in the vfollcvvin'g manner-1 In a system for handling the calls of N talker-'synth M channels iM N a number MN 'of vgates lis provided, each of which 'corresponds jte a particular che cf the N talkers 'and to 'a particular ene of the M channels. It is 'ac- 'ti'ated by the coincid nce o'f three stimuli, name#- f.

ly l(a'the occurrence of a'rst cyclically recurring e'pcch allotted to this particular talker, -(b1) 'the 'occurrence of a second cyclically recurring epoch allotted to 'particular channel, and (c) the l'activity of the talker iii the ffcrm 'of a spurt 'of speech. Furthermore, thes.` kstimuli actuate this gate only when the 'particular channel is' then idle and a't the inception of the particular talk-'- ens-speech spurt. When so actuated, itV (a) establishes a speech path from the talker to' the channel, which h'olds until the 'conclusion of the talks'purt and is 'then released; (c) prevents 'the establishment of a similar path from this talker to any other channel; rc) Ypnt/ents the establi'shment 'of a 'similar path from 'any other talker 'to zthis'channel; and (d) initiates 'a vst'art signal lwhich, purely on the basis of the instant Within :the repetition 'cycle at which it occurs, idehtiii'es `bfoththe talker and 'the channel and so provides 'informaticn from which the receiver apparatus can route the incoming call 'to the listenerfrorn vwho-m it is intnded. At the receiver end vci" the system', similar apparatus, stimulated b'yj'oint Occurrence 'of (d) the start signal, (b) an epoch alltted to thel particular listener; (c) an-p'octi ses 2 allotted. to the particular channel, performs the routing. l i p It 'is a feature "of the invention that the idntificationrof a particular combination of talker (or listener)` and channel is carried out on a pure `time' 'assignment basis.

It is another'feature of the invntion that the "several channels 'are offered in rotation to each of the' talkers in turn, so that a given instant in the time constitutes a unique identification of a particular talker 'and a particular channel-a combination which occurs once and only once in the repetitionv cycle of the systlm.

It is another feature' of the invention that the time assignment' of Vthe several channels for the purposes-f the present TASI (Time Assignment Speech Intrpolation) system may be identical with that for 'a TDM `(Time Division Multiplex) `system with which it is cooperatively related, and that common timing apparatus may lbe employed to serve both purposes, both at thev trans- Amitter'end of thesystem and at the receiver end'.

It isstill'another feature of the invention that the time relations may be assigned, as between the TASIlsystem Aand the TDM system, in various Ways; for example, two TASI systems, each `'capable of handling the calls Vof N talkers on M channels, may be interconnected with a single TDM 'system adapted for transmission over 2M channels. Other numerical relations Aare equally possible.

The invention will be fully apprehendedv from the following'detail d `description of 'a preferred embodiment thereof, taken` in connection With the 4appended `dravv-ings, in which:

Fig. 1 is a block schematic diagram showing two independent TASI systems, 'each handling fourteen talkers with six channels, both served by a single twelve-channel TDM systzm;

Fig. 2 isv av block schematic diagram vof TASI transmitter apparatus;

Fig. 3' isa wave form diagram of assistance in explaining the'operation of the system;

Fig. 4 is a block schematic diagram showing the interconnections among the units of the transmitter apparatus of a TASI system, for a single talkr and `a 'single channel;

Figs. 5, 6, 7, 85, and Q'are circuit diagrams show- 'in'g details df ertain o'f the components of Fig. 4;

Figi 10' is a block vschematic diagram of TASI receiver apparatus;

Figi. 1-1 vis a block schematic diagram showing the interconnections among the units of the receiverapp tus of a TASI system, for a single 'c'liainelia'd -sfingle listener;

Figs. 12, 13 and 14 are circuit diagrams showing details of certain components of Fig. 11; and Fig. is a wave form diagram of assistance in explaining the operation of Fig. 12.

Statistical studies of telephone traic have shown that, during any given telephone call, the facilities are idle the greater part of the time, and that, if a channel were to be assigned to a talker only during the brief talkspurt intervals when the talker is active in the sense that speech sounds are actually being produced, and at the conclusion of the talkspurt were then to be reassigned to another active talker, a given number of channels could handle the calls of a greater number of talkers. nels could handle the calls of seven talkers, six those of fourteen, ten those of thirty-two, twelve those of forty, and so on. The invention to be described in detail below provides for such handling of the calls of a number of talkers by the facilities of a lesser number of channels, the assignment of the several channels among the active talkers being carried out on a time basis. It will be apparent from the description which follows that the complexities of the TASI apparatus are considerable. The required apparatus increases in approximate proportion to the product of the number of talkers by the number of channels. Therefore considerations of apparatus economy may dictate a plurality of smaller channel groupings, such as two fourteen-talkersix channel systems; instead of one forty-talkertwelve-channel system, supplying a single twelvechannel Time Division Multiplex system. Thus Fig. 1 is a block schematic diagram showing two fourteen-talker-six channel TASI systemsli, I2 feeding a single twelve-channel TDM system i3 at the transmitter terminal. At the receiver terminal, the twelve TDM channels are iirst broken down by a TDM receiver Id. into two groups of six, the channels of each group being then sorted and routed by one of the two TASI receivers i5, I@ to the correct listeners among the fourteen of the group. Thus the economies of the systems may be separately treated, while from the standpoint of transmission of information, the interconnection between the systems is entirely satisfactory.

Fig. 2- is a block schematic diagram of one fourteen-talker-six channel (hereinafter designated 1li/6) TASI system in which, to avoid excessive complexity. apparatus details are omitted. They will be discussed in connection with the figures to follow. A rst pulse distributor having twenty-eight output leads is symbolized in the gure by a commutator Il of twenty-eight separate segments and an arm I8 which rotates over them and in doing so applies the voltage of a battery i9 to each one in succession. The fourteen oddnumbered segments are associated with one TASI system (the upper one Il in Fig. 1) while the fourteen even-numbered segments may be associated with another TASI system, for example the lower one I2 in Fig. 1.

The talkers may be considered as being arranged in a horizontal row, and numbered A, B, C N. Each talker is provided with a conventional telephone transmitter, the output conductors 29a, 2gb, etc., of the several transmitters dening the Vertical conductors of a cross net. The six channels over which these talkers calls are to be transmitted define six horizontal conductors 1, 2, 3, 4, 5, 6 of the cross net. Associated with each crosspoint of the net is a Gate II 2l which, under precise conditions to be Specically four chan-Y fil f the channels 1 to 6, inclusive.

defined, establishes a communication path from a talker to a channel.

The talkers may be conceived of as talking or remaining silent at will, their activity distribution being, and changing, in a random manner. Activity of each talker is recognized by a conventional speech detector 22a, 22h, etc., which continuously monitors that talkers speech and determines whether or not it exceeds a preassigned critical amplitude. If it does, the speech detector 22 gives a steady on signal in its output circuit. Otherwise it gives a steady off signal. Thus it determines at every instantJ whether or not the .talker is in need of a transmission channel. Voice-operated relay devices having these properties are well known and need no further description.

The output of the speech detector 22 constitutes one input to a Gate I 23. The other input to this Gate I is a train of pulses from one of the odd-numbered segments of the distributor il. Each Gate I is arranged to deliveran output voltage of standard magnitude when, and only when, it receives inputs concurrently from the speech detector and from the distributor.

Each Gate I is associated with a vertical column of Gates TI 2i. When the output signal of the Gate I exists, as described in the preceding paragraph, the Gate I delivers it simultaneously to all the Gates II of this column. For example, if the Gate I in question is Gate iA 23a, its output is applied to the Gates II of the iirst column by way of the conductors 24a, 2da-i, 24a-2, etc. The talkers telephone instrument associated with the same Gate I is also connected by way of the conductor 28a and its branches to all members of this vertical column of Gates II. (Hereinafter the difference between a talker and. his instrument will be disregarded.)

A third input to the several Gates II is derived from a second distributor of twelve output leads, symbolized by a twelve-segment commutator25 having a rotating arm 26 which applies the voltage of a battery 21 to these several leads in succession. Those numbered one to six, inclusive, are associated with the six channels of the present TASI system (the upper one in Fig. 1) while those numbered seven to twelve, inclusive, may be associated with another TASI system, for example, the lower one in Fig. 1. Thus the battery voltage from each particular segment of the lower distributor is applied in th-e form of a pulse simultaneously to all of the Gates II of one and only one horizontal row associated with one of Thereafter, a similar pulse is applied from the next segment of the lower distributor 25 to all the Gates II of the next horizontal row, and so on to the sixth row. Pulsing of the Gates II of the system i shown then pauses while similar operations take place with respect to the lower TASI system 2 of Fig. 1 due to movement of the rotating arm over segments seven to twelve, whereupon the whole cycle of operations is repeated.

It is advantageous to complete the pulsing cycle for all the members of each vertical column of Gates II, corresponding to one talker, before commencing the pulsing of the Gates II of the next column, corresponding to another talker. To this end the pulse outputs of the two distributors may be arranged on the time scale as shown in Fig. 3, where designations t1 indicate pulses of the talker distributor Il and designations t2 indicate pulses of the channel distributor 25, Thus, for example, ti-C designates Vf-As showniniithej lower partrof :the figure: each tffpulsejperiodzo 62:5nnicrosecondsisdividedjinto esix '.fequakpartasdf .10 .Axmicroseconds Ilength. Vvl-'Io V:eaf'xh :of :.thesepar'ts :corresponds ia s single output rplsero'f the :channel distributorrz. 'The-:occur- :rence times fof these pulses .'fare: designated ta :a esecond :suhscriptindcating which :one `:of the :rstfsixztz pulsesrismeant. .Thus 132-12 `=indicates the :t2 pulse l'which mon-stitntes one of ethe :two 'inputs .to .all of the Gates [1 `which :sen-ve the secondnhannel s2.

1th this pulse distribution every instant :of :the-:timescalefisiuniquelysassigned toifa particular :and la @articular vxcharmel. :For example, itlre v -instant.:marked non FEig. L3 `by 'the :arrow is :channellfNdZ .'A-tithis instant allhf.- theiGateslII sof `the third vvertical :,:column are :partially eniabled zby `fthe fit1-1C :pulse ir-if 'talker C .is encomen- `etarily active) :fand-jallcofr. the `Gates II-.ndfqthe-second horizontalfrowaregpartially :enabledbyuthe -t2-.2

apulse. Thus onlyfpne GatelIIfis enabled ink'both senses, rand? thisiis 1 the l: Grate, II designated fC-2 ;in Eig.2. fWhemthisfGateiIListhusfullyenabled :itsperforms the lfollowing Junctions: K

r1. The signal pathf'is completed fromitalkerf() :to channel JN0. ,12,and1theparticular Gate II is fdisabledgfrom frecognizing :la-ter epulseswef v'the t2 train, 'during the contnuancefof the talkspunt;

2. -Alllthirte en other-Gates II of l the same horinzototal. row :are .disabled from accepting tifpulses.

AIhisgprevents-.assignmenttoi.channel-Nor-Z to :any other stalker;

3. `All ve other zGates-:ILof the -vsame -vertical column -are "disabled "from kaccepting y.t2 pulses This prevents .assignment fof =.talker aC sto -any other channel; and

'A "'start eSignal is generated, eyhosel-exact .flocationzonthe ltime:.'scalefservesfas 'fanJ indication .fito the receiver frhy iwhich l"the'particular Y:talker KC) rand 'the panticu'lar 'f1-channel A(f2) may flue.A

'z-identied, so that stalker ACs-rcall may f'fheiicorfrectly routedctoglistener iC.

drawn for the condition liniwhichxchannl'No.2 isi fmlade `"available :to talker rlC, the pulse fsource shown ,i in Fig. 2 zcommntator :l'i may be asa rtwenty-eightzstage@ringfeircuitsdf which Valterizrate @output conductors fsupplypulses v:to :the :several 35 :Gates :I. Ilhe frdetails :,:o `such t ring :circuits 'array be, for example, @as :described fandshown inffan VVapplicationsufi E. 4Ii/I.Roschioe, SerialN'o. 7935746, :filed Decenib erf-24, :A1947 :and issuedApril'l,T1950, tas,alatent1255043354. ,fInthepresent'examplethe isixthrstagef-may @be connectedv to.g Gate I-'C.

The s ring Y:circuit must :operate fin "synchronism #with `vandther Vrr'in'g f'circuit 25 fo'f f`twe1ve-fstages, 'which supplies itz ipulses *from fits v'various @output l:wratyato :assure .suchfsynchronismsis ato-drivelheiih of fthemfromea common source.,

'.,Theftwelveistagering; rnayfiisV desired, -Joefdriven -by fa Abasic aiming esource. In order ato atiefthe ,-TASI ysystem into sa TDM system,A--forQeXamplefea fBCM rpulse cod-e modulation) z-systern, however, the-:basictimingfsource cf thePCM system, avhose frequencyis that yof the basic ipulse frrepetition rate, -may be .made -to do :double 4duty. Ifhusva basic timingsourcea'i whichmay include afvcrysital-controlled .oscillator may .deliver pulses @fall microseconds*durationerecurringr'at .6,72 klocycles wpensecorld to van Inserter .Unit 4Whosey details and ;function's -will be fdescribed below; andit :nay ialso kdeliver Athem to y:a suitable frequency sstep- .down-,uniti :suchas -=a multivibrator-ofthetype -describ.ed in VUnited States Patent 2,022,969 sto i L. :A Meacham. Thestepdown'ratioof thisunit may-libeequal to the numberfof digits :employed inithe' code. Thus t for :a seven-.digit cede zwhich i-has;b.een found satisfactory, itsiratiofis'f'? to 1. 4The output ypulses Lof this yunit therefore have fa ,lrecurrence rate :of

r kmsec. `;Application'tofipulses of `t'his'cafreduencytothetwelvefstage `ring produeeshutput rpulses therefrom @vrhich recur :at this -Lfrequency samongtheiseveral outputileadsrbut `which,-"omfany one lead; recurtat zorSikci/sec.

The 961fkc;sec.zpulses ,areaalsoJappliedfto a i frequencyF dividerv 32 `which;l again: may7 be zal. multifvioratonas disclosed in thefMeacharn patentiere- Lferred .to above. Thenutput pulseff-requency .of

thisuniunamel-y lor 16 kc./sec. is now applied to control the-twentyfcghtstage rin-g 7V?. ,This results in-outputpuises aoicthelatterl which. recur: at '.1 fkcg/ sec.- amongst/he several .output f-leads sor .at 8 `lie/sec. :as between `successive even-numbered; output leads butwvhich, eonanyaonelead,,recurat forlfl 1- cycles peresecond.

`Correct zphase .relations among -the .output tpulsesaof .the l.two ring .circuits and .the various stepdown multivibrators, as .well as larnongs other :similar Aunits in other ZA.parts of the system, may .be assured in any desired .vs/ay, .ior example, a rphase coupling -as explained l in :the aforemenn r-tioned-applicat'on ofV E. M. vRosch1:re, 1.and omitted ifromfthe drawings .-.to. avoid Y'undue complexity.

H.The.operation .of the'lsystem' Vwill now foe-*1described sin detail under the conditionsl in which stalker A ,is foccupying ichannel ',No. l, ftalkerrB eis: occupying l channel ,No 6 the '.remainingztalkers sare silent,iandechannelseztoz,v inclusive, areidle. 'Assumeznow that talker@ swishesftotalk 'with llistener -rC fanyerequiredgswitching :operations-zare assumed to have been otherwise talcenzcarevof zalreazd :ro'f the system .presently being: described) h1 the :course '.'of AtheLintialLrSe of fthe iirstrspurt which monitors his voice energy recognizes the fact that his speech level has exceeded a certain preassigned value and gives a steady on signal in its output circuit. The speech detector output may consist of a negative steady voltage of l volts or so on the output lead 24e during the absence of a talkspurt and zero or positive voltage for the speech on condition. Referring to Fig. 5, the on signal from the speech detector enters the Gate l-C 23e which may comprise a direct current coupled multivibrator comprising tubes 35 and 36 and having two stability conditions, determined by a negative bias of the order of volts on the grid of the left-hand tube 35. In the off condition, the right-hand tube 36 is conducting, the left-hand tube is non-conducting. The positive voltage of the speech detector output is applied to the grid of the tube 55, thereby raising this grid from the negative potential of its bias source toward cut-off. This negative bias of the grid of the left-hand tube is arranged to be greater in magnitude than the speech detector output voltage so that this voltage alone is insufficient to trip the multivibrator, When, however, the third t1 pulse of the series of Fig. 3, namely, the one designated tr-C occurs, it is applied by way of a blocking condenser 3l to the same grid. It has a magnitude of the order of +10 volts and, when added to the voltage output of the speech detector, is sufficient to trip the multivibrator to its other stability condition. Immediately, the tube 36 ceases to conduct and its anode potential rises. This anode potential is applied to the control grid of an amplifier, for

example a cathode follower 38, whose output is thus a positive voltage which is applied as one of the two control inputs to the Gate II in question, namely, the one shown in block form, Fig. 4, and designated C-2 in Fig. 2.

At the first instant of the commencement of the t1 pulse in question, no further input signal is applied to this Gate II because, as above assumed, the No. l channel is occupied by talker A. However, after the lapse of 10.4 microseconds, the t2 pulse associated with the No. 2 channel occurs and is applied as the other input to the Gate II in question.

Referring to Fig. 6, which shows the circuit details of the Gate II, this 752-2 pulse is applied to Gate II by way of a condenser 49 to the control grid of a tube 4l which is a cathode follower amplifier having a common cathode resistance 43 with the tube 42. The control grid of the latter is biased to hold its cathode slightly above the tube cut-ofi and the tube therefore acts as ampliiier of the output voltage of the tube 4l as it appears on the common cathode resistor 43. It passes this pulse by way of a blocking condenser 44 to the grid of a double stability multivibrator of two tubes 45, 46, the anode of each being coupled by a resistor and a condenser to the control grid of the other. Prior lto the arrival of the t2 pulse, this multivibrator is 1n its quiescent condition in which the left-hand tube is non-conducting and the right-hand4 tube 46 is conducting. This condition is maintained by a positive bias on the control grid of the right-hand tube which is the resultant of a greater positive Voltage from the plate of the left-hand tube overcoming the normal negative bias, and a negative bias on the control grid of the left-hand tube.

rIhe positive voltage output from Gate I is applied directly to the control grid of the lefthand tube 45. The magnitude of this voltage the tube 42.

and also the magnitude of the t2 pulse output of the tube 42 are so adjusted that individually neither one is suiiicient to cause the multivibrator to change its condition ofy stability. However, the sum of the Gate I output voltage and the t2 pulse voltage from the tube 42 are sufficient to cause the multivibrator to trip, whereupon the left-hand tubev 45 becomes conductive and the right-hand tube 46 becomes non-conductive, a1- lowing its anode potential to rise.

The resulting positive voltage increment from the anode of the right-hand tube 46 performs four functions.

First, the rise in'voltage at the anode of the right-hand tube 46 of the multivibrator overcomes the negative bias voltage at the suppressor grid of a tube 41 to whose control grid the voice signal originating with talker C is being applied by way of a condenser 48. Prior to overcoming this bias, the tube 41' constituted substantially an open circuit in the voice path. Operation of the multivibrator 45, 46 to overcome the bias of the suppressor grid of the tube 41, however, enables it to amplify the voice signal and pass it by way of a blocking condenser 49 to the output terminal 56 of the Gate II. This output terminal is connected to the No. 2 channel. The abrupt wave front of the switching voltage from the anode of the tube 46 may be'vsloped and delayed by the constants C and R 'in the suppressor circuit to reduce the audio click. Additionally, this same rise in voltage o f the anode of the tube V46 is transmitted to the control grid of two cathode follower tubes 5I and 52 which are preferably alike and have individual cathode resistors 53, 54 of like value. ThusV the outputs of these two cathode followers are substantially alike in magnitude and sign. The cathodes of these two tubes are interconnected by way of two rectiiier units 55, 55, the midpoint 5l of the pair being connected to the control grid of the tube 42. These rectifier units are connected for conduction in the forward direction toward the mid-point 51. Thus a positive voltage is applied `to the grid of Its cathode follows,`and the cathode of the tube 4l which is directly connected to it rises above cut-off, thus disabling the tube 4| from recognizing further pulses of the t2 train. Thus the particular Gate II is in eiect frozen in its condition of connecting talker C with chan'- nel 2. l

Second, the output voltage of the right-hand cathode follower 5I is applied to all 13 of the Gates III serving the No. 2 channel. All of these Gates II are alike in construction and all contain cathode follower tubes connected in the manner of the tubes 5I and 52, and all fourteen of the cathodes of the right-hand tubes of the Gates II of the second row in Fig. 1 are connected together. This prevents assignment of any talker other than C 'to channel No. 2.

Third, the output voltage of the left-hand tube 52 is applied in similar fashion to the cathode resistors of similarly connected cathode follower 'tubes of ve other Gates II of the same vertical column.v The interccnnectio'nof the Gates II'for these purposes is shown in Fig. '7.

` As a consequence of these connections, the coincidence in time of a voltage applied from, Gate I to the grid of the left-hand tube 45 of the multivibrator results in disabling all other Gates II of the third vertical column, thus signalizing the fact that talker C is active and is being assigned a channel, and also in disabling all others of the Gates II of the second horizontal row, thus sigpotential of the right-hand tube 89A. rises.

nalizing': the factI that;- channel 2is.fbusy. Thus.: assignment oftalker'C'to-any channel otherthan No'.` 2,.and: assignment ofv theNo. 2 channelto, any other talker are' both prevented. On the; other'hand theoppo'sitely poled.rectiiiers 55 servetcprevent the disablement oi another Gatev II'of the same verticalV row from disabling those; of f the' present horizontal row,v and vice versa. In addition, whiletheGate-Iihas been enabled:V bythe time coincidence of theY output of. GateI` and the: arrival i thet'z--Zpulse at the grid` oithe tub'e lil, disablingoffthe; tube byfappl-ica'n tion-of voltage from the poi-nt'fto the'gri'dwi.. the'I tube 42 preventsv further pulsesi- 01- the.; 152; train from in'- anyway alteringV the situation.-

Fourth, the'voltageof the -ca'thodeof thetubef V4- which; as aboveexplained..v is; appliedl to cut oil? tzpulsesfrom the thirteen other Gates II-o*l the same'horizontal row'vis alsoi appliedtoxone input point of' a start signal generator4 (Eig. Sfr: for use in generating a start pulse whichgis'the same for all channelsa-nd identies-aparticular talker' and-a particular channel-by; Virtuefofthe precise instant of the cycle atwhich it istrans-A mitted.

Eig. 8 shows the the circuitdetails ofrthe start signal generator. This unit has six inputpointsf ofrv which the first 6I isconnected toall-our-v teen of the cathodes of the tubes 51 of'theGrates` II of the rst horizontal row,y the second 62 to.k all fourteen. of z the cathodes of the tubes of Gates II of the second. horizontal row andA so:- on through the. sixth input point 65. Thus-the'. abruptly rising voltage atthe cathode of the tube l. of the Gate II-under considerationisg applied to the second input point 62 of the start. signal generator, which is connectedby Way of a resistor. 68 and a condenser 69- to'the-griduof a. tube 12 which is'biased negatively The other input` points. arey similarly connected to. ar1.RC. networkA and to the negatively biased grid or aftube. The anodes of these `tubesareall .sup` plied by way. of a common anode resistorI '|3-. from a common potential source. The abruptly rising voltage.appliedtoanyof theseinputpoints, and in particular to the No. 2 input point 62, is differentiated by the resistor condenser cornbination, whose elements 68,99have appropriate Values for this purpose, and passed by way of the. anode'of thetube 'i2 and a coupling con.` denser 'M to the grid of a tube 'i5 as a negative pip 'IS by reason of the4 phase invertingeiect of the tube 12. The tube 15, whose grid is-biased somewhat above cut-off, reinvertsthis pipv and passes the signal as a positive pip 'l1 of about 20- volts amplitude by way. of a blocking condenser-19- to the gridof `one tube 19 of a. single-trip multivibrator which comprises two tubes 19 and 89 having a common cathode resistor 3| and: a condenser 82 coupling the anode of r the tube 19.*. to the control grid of the other tube 8E). As is well known, when suitable biases are applied to the grids, suchas +15 volts on'the grid of the left-hand tube 19 and. +25 volts on the grid of the right-hand tube 80, .the quiescent condition of this circuit is that in which the. tube 19 is non--conclucting and the tubeB!) is con-f ducting. Application of thepositive'pip 1T to the grid of the tube E9-.causes the cirouitto trip over to its opposite conditionA of stability in which the tube '19 is conducting, and the anode The circuit snapsback to thel original conditionafter a. time determined by the values of the coupling condenser 82 and the. cathode resistor 8l. Such single` tripmultivibrator circuits are` well know-rrn andare described, forexamplain Time Basesf."

present invention, comprises ia collector 9 Lwhichv takes samples, in rotation, of the. speechenergy appearing] atits: twelve.` input terminals,` and a. coderr 92A which. transforms each. of these samples into. a. 7-digit pulse code group, and'.

delivers. the. resulting.- pulse trainy at its output. terminals; In the, presentcase the basic pulse repetition rate is 672.-.kiocyc1espersecond. With seven pulse positions per sample, anynumber up to. seven of. these `pulse positions being filled, the. successive sample. rate is 96 kilocycles per second. With- .twelve vchannels in the system, the. sampling rateforeach channel istherefore eight4 kiloeycles per second-,whichas.above explained is alsotherate ofy transfer from talker to talker.. in. the TASI. system.; In the ordinary system, the twelve channels. connected. tothe twelve. inputpointsA of` the; collectorI 9|.. are.. examined-in rotation forf activity4 of the. several'talkers .who are associated. with these channels on a onefto.- one basis, .andthe sampling.. rater is. selected. as y8` 1re/sec.y because.A it.is twice the highest voice. frequency,l required to be transmitted. As is wellv known, .withthis selection, degradation of 'speech quality by the. sampling. process. is. negligible. When. theimprovementof the present invention is introduced,- the same.twelve channels are ex.-

amined. for activity byY the same sampler, which activity;v may now be. thatof any six-of. the four.- teen talkers-.Ato N vfor.the..f1irst..si-x channels and. any.- six of.the other. fourteen. talkers A.4 to..N"' for the: second. sixchannels` In orderr to. hold. thereceive-r. apparatus. in perfect .y synchronism with. the. transmitter. apparatus,A which is` required for intelligibility and correct routingeof the. decoded. messages, a suitable. framing.. signa1.may. be generated at' the transmitter; .under control of. the timing .source 39- as by a-.generator 93`land.. the framing signalmay be interspersed. amongthe.codepulsegroups cr otherwise addedv tothe .outgoingpulse train. A. suitabler framing signal. and.` apparatus.. for. generating. it atthe transmitterandior recognizing andutilizingit atthe receiver. are described. in an application-oid.. G. .Kreer and. Peterson, Serial. No. '7-76,280,.led.September 26, 1947, and` issued Octoberl, 1959, as-Patent 2,527,638.. The resulting pulse train...may then be regenerated. prior` toftransmissionas.. by slicingpulses at a preassigned tlevel .andgatingthem `at.preassigned times. Suitable regeneratingl apparatus based on thisprincipleis described-.in an .application `rof L. A.. Meacham-,..Serial-'No 772,913, ledSepsig-nalthe. RCM-.pulse tra-in-may. beacccmplished in many ways, a particularly simple one being to apply the start signal pulse in opposite polarity to the code pulses, to a high impedance point. Thus, referring to Fig. 9, negative PCM pulses from the coder 92, the framing signal l0! from the generator 03, and the positive TASI start signal 33 from the output of the start signal generator of Fig. 8, are all applied to the control grid of a tube |0f. This tube has its anode and cathode directly connected to the `anode and cathode of a gating tube 05 to whose grid 572 kc. gating pulses |01, from the timing source 30, are applied. A third tube |06 has its cathode directly connected to the cathodes of the first two tubes |04, |05, and its anodeis separately supplied, while its grid is coupled to the anode of the tubes |04, by a condenser |08. A single cathode resistor |055 connects all the cathodes to a point of negative ixed potential. Mean potential levels may be stabilized by the use of point contact rectifiers H0, ill, i l2, in the grid circuits in the manner shown. In the quiescent condition, one or both of the left-hand tubes |04, |05 is conducting, while the right-hand tube |05 is cut off. As explained in the foregoing application of L. A. Meacham, Serial No. 772,913, this circuit trips from a first condition in which the righthand tube |05 is non-conductive to a second in which it conducts when, and only when, negative pulses are present on the grids of both of the rst two tubes 10d, |05. When the start signal 82 is present, being of opposite polarity to the PCM signal pulses |00, it masks the latter, and prevents their application to the grid of the rst tube |04. The gating pulses |01, applied to the grid of the second tube 05 are insufficient, when alone, to trip the circuit, so that the outgoing train of regenerated pulses H5 contains a blank of 10.4 microseconds or seven pulse positions duration. In case due to differential'time delays in various parts of the system the commencement of the blank fails to coincide with the first digit pulse of a code pulse group, this may easily be cured in well-known fashion by the addition of a small time delay either to the PCM pulse train or to the start signal, whichever occurs earlier.

In the foregoing there has been described lthe establishment of a signal path from talker C to channel No. 2, starting at the inception of his talkspurt, the generation and transmission over the pulse code modulation transmission system 'of a corresponding suitably chosen start signal,

the marking of talker C as active, and the marking of channel 2 as busy. This condition continues as long as talker Cs present talkspurt continues. Meantime, similar operations may take place with respect to any of the talkers other than A, B and C, and with respect to any channel other than Nos. 1, 2 and,6, which, under the presently assumed condition, are busy. These operations can be multiplied until all six of the channels are carrying the conversations 0f six out of fourteen of the talkers A to N, while at the same time all six of the other TASI system (the lower one in Fig. 1) are carrying six conversations of talkers A' to N.

Now when any talkspurt ceases, the corresponding talker returns to the inactive class and the channel which he has been occupying must be rendered available to another talker. To describe the necessary operations, assume that talker C is the rst to cease. On the reduction of the level of his voice below the preassigned threshold at which the speech detector 22o (Fig. 4) recognizes him as active, the speech detector ceases to furnish a zero or'positive steady on voltage and furnishes instead a steady negative off voltage. This negative voltage is applied to the control grid of the tube 35 of the multivibrator of Gate I and returns the multivibrator to its initial condition. Tube 35 of this multivibrator therefore commences to conduct and its anode voltage falls, thereby cutting olf the cathode follower tube 38 and removing the positive voltage output of Gate I from the grid of the tube 45 of the multivibrator of Gate II. This multivibrator thereupon returns to its quiescent condition in which the tube 46 is conducting. The anode of this tube 46 therefore falls and so reduces the potential of the suppressor grid of the tube 41 below cut off. This in effect opens the Voice current between talker C and channel No. 2. At the same time the negative voltage applied from the anode of the tube 45 to the grid of the cathode follower tube 5| removes the disabling positive voltage from the other thirteen of the Gates II supplied by the lf2-2 pulse and the removal of the positive voltage from the grid of cathode follower 52 likewise removes the positive disabling voltage from the other five ofthe Gates II of the same vertical column. Lastly, removal of the positive voltage from the grid of the tube 42 of the present Gate II removes the positive cathode voltage from the tube il and thereby permits the tube 4| once more to receive t2 pulses. Thus, all of the Gates II of the second horizontal row in Fig. 2 and of the third vertical row, including the Gate C-2 in question, are once more enabled to accept speech spurts from other talkers, or a new speech spurt from talker C, whichever occurs earlier.

The receiver apparatus by which calls from each talker are properly routed to the corresponding listener will now be described in connection with Fig. 10. Referring, however, again to Fig. 1, there may be two TASI receivers each arranged to handle incoming calls arriving by way of six channels and intended for any six of fourteen talkers, both associated with a single twelvechannel PCM or other time division multiplex system.

Referring now to Fig. l0, a talker distributor |50 of twenty-eight channels and a channel distributor |5| of twelve channels are provided. Each distributor may comprise a ring circuit similar to that employed -at the transmitter. The distributors are symbolized in Fig. 10 as commutators in the same manner as in Fig. 2 for the transmitter. Thus odd-numbered segments of the first distributor |50 are associated with the various listeners LA, LB, LC, etc., of the upper TASI system of Fig. 1, while the first six successive segments of the second distributor |5| are Vassociated with the rst six channels 1, 2, 3, etc. of a twelve-channel PCM system. As in Fig. 1, even-numbered segments of the first distributor |50 and the segments numbered six to twelve of the second distributor |5| are associated with the talkers and the channels, respectively, of the second TASI system of Fig. 1. These distributors may be driven by pulses or appropriate frequency derived from a timing source which is held in synchronism by any desired means with the generator at the transmitter. Thus, referring to Figs. 10 and 11 together, a basic timing generator |52 delivers pulses at a repetition rate of 672 kilocycles under control of a synchronizing component of the incoming pulse train to a 7/1 frequency divider |53 whose output pulse rate is thus 96 kilocycles.

. 13 The output pulses 6/1 frequencydivider |54 whose output `pulses drive the listener distributor l`| 50. `The-output pulses of the 7/1 divider |53 also 'drive the channel distributor and in addition, a 2/1 frequency divider |55 which controls a Start Signal Recognizer |55. Referring'to Fig. 11, which is drawn for the condition in'which a message on channel 2 is routed to listener LC, the listener distributor andthe channel distributor |5| may be ring circuits, of twenty-eight stages and of twelve stages, respectively, -similar to the corresponding distributors |1 and 25 at the transmitter terminal. Theseveral'ring circuits and frequency dividers may be held in proper phase in the manner above referred to in connection with Ysimilar apparatus at the transmitter terminal. The pulse output of the talker distributor |5|lmay consist of a train of fourteen t1 pulses identical with those of the transmitter and similarly spaced apart, and the pulse output of the channel distributor may consist of successive trains, each of siX t2 pulses, all the pulses of a train lying within a single t1 pulse interval as in the case of the transmitter. The timing relations illustrated in Fig. 3 apply to the receiver equipment as wellas to the transmitter equipment.

The fourteen listeners LA, LB, LC, etc., may be conceived of as being arranged in a horizontal roW and the six voice channels in a vertical row. The listeners lines and the incoming channels thus define a cross net, at each crosspoint of which is a Gate IV |50 whose functionit is to route a message arriving on the channel with which it is associated to the listener with which it is associated when, and only when, it is intended for him. This function is accomplished on a time assignment basis in the manner to be described. To this end each Gate IV |50 receives two enabling pulses, rstly a t1 pulse from one segment of the listener distributor and secondly, a t2 pulse by Way of a Gate III |6| one of which is associated with each channel from the channel distributor |5|. The Gate III, however, supplies its pulses to the Gates IV only when it has in turn been enabled by a Start pulse from a Recognizer |56.

The operation will be described in connection with Fig. 11, in which the frequency dividers and the ring circuit distributors referred to above are shown schematically. The 2/1 frequency divider |55 may have a two-phase output. It may be a multivibrator of tWo intercoupled triodes, an output lead being taken from the anode L of each.. The wave forms of these voltages are indicated in curves a and b of Fig. l5. These voltage Waves are individually diierentiated and sliced yby the units |51, |58, to provide the supplementary waves indicated in the curves c and d of Fig. l5. Referring to Fig. 12 which shows the circuit details of the start signal recognizer |55, the incoming train of PCM pulses, which have been combined with framing and synchronizing signals in known fashion and into which the TASI Start signals have been inserted in the manner described above, is applied, after regeneration, amplication and inversion as de'- sired, in the form of a sequence of positive pulses to the Recognizer |55 by way of a condenser |15 to the grid of a cathode follower tube |1|. The anode of this tube'is connected to a. source of positive potential,l itscathode resistor is connected to a source of'negativepotential, and its grid'is 'connected'by' Way of 'a varistor |12 to a animee of 'this turn Ydrive a point of intermediate negative potential such as -23 volts. The waves a andb, derived from the two-oppositely phased output points of the 2/1 frequencyfdivider |55 are similarly applied to the grids of similarly connected tubes |13 and |14. The cathode of the tube |13 is con-v nected by way of a resistor |15 and a varistor |16 to the cathode of the tube 51|. The cathode of the tube |14 is similarly connected by way of a resistor |11 and a varistor |18 to the cathode of the tube |1|. By suitable choice of the tubes |1I, 13, |14, the magnitudes of their cathode resistors, and the potential of the sources to which their cathodes and grids are connected, the potentials of these cathodes in the absence of input pulses may have values of -20 volts.

The point |19 at which the resistor |15 is connected to the varistor |15 is connected by way of a condenser |86 to the grid of the left-hand tube |84 of a single trip multivibrator of conventional form. This grid is connected by way of a varistor |86 to a point of negative potential, and the grid of the other tube of the single trip multivibrator is connected by way of a varistor |81 to a point of less negative potential. Thus, in the absence of input pulses, the righthand tube |85 is conducting and its anode is held down in potential. The point |8| which is common to the resistor |11 and a varistor |18 is similarly connected by way of a condenser |82 to the-left-hand tube |30 of a similar single trip multivibrator whose cathodes and grids are simi larly biased. Thus, in the absence of input pulses, the right-hand tube |9| is conducting and its anode is held down in potential.

If incoming PCM pulses were to arrive at the grid of the tube |1l unaccompanied by the a and b waves at tubes `V|13 and |14, they would have no effect on the tubes |84 or |95, because under these conditions the varistors |16 and |18 are in their high resistance condition, and the PCM rpulses are thus effectively insulated from the grids of the-.tubes |84 vand |96. Likewise, if the waves a and b are applied to the tubes |13 and |14 Without the application of PCM pulses to the tube |1 I, the cathodes of these tubes rise in alternation from 20 volts to approximately ground potential, but the associated varistor |15 or |18, as the case may be, is by the same token drive-n to its low resistance condition so that, again, the grids 0f the tubes |84 and |90 continue t0 be held at low potential. But when PCM pulses are applied to tube |1| at the same time as the waves a and b to the tubes V2 and V3, then, during the A period (Fig. 15) when the cathode of the tube |13 is held up, the rst PCM pulse of the associated pulse group raises the potential of the cathode of the tube 51|, drives thevaristor |15 to its highA resistance condition, and applies a pulse to the grid of the tube |34 which trips the multivibrator |84, |35 to its other condition of stability, and the anode voltage of the tube |85 rises. This condition holds until the conclusion of the ensuing B period, when this multivibrator vis restored to its original condition by the application of a poitive pulse of the wave 4c to the grid of the tuber |35. Such restoration is possible because the grid of the tube |84 is no longer held positive by the cathode output of the tube |13, since throughout the B period the a Ywave at the grid of the tube |13 has its low potential value. By exactly similar action, the occurrence'of lPCM pulses in the B Vperiod trips the multivibrator-on the occurrence of the ilrstiPCM l pulse to arrive, causing the anode potential of the tube |9| torise.

The anode of the tube |85 is connected by way of a varistor |95 to the grid of a tube 200, and the anode of the tube |91 is similarly connected by way of a varistor |96 to the grid of a tube 20|, whose anode and cathode are connected directly to the anode and cathode, respectively, of the tube 200. The wave a, as derived from the cathode of the tube |13, is also applied by way oi a resistor |91 to the grid of the tube 20| while the wave b, as derived from the cathode of the tube |14 is applied by Way of a resistor |98 to the grid of the tube 200. The actions of the combination of the resistor |98 with the varistor .A

|95, and of the combinvtion of the resistor |91 with the varistor |96 are similar to the actions of the combinations described above, such as that of resistor |15 and varistor |115, namely, to apply positive voltage to the grid of tube 200 or only when positive voltage is applied by both paths, the varistor and the resistor, and to apply negative voltage to the grid of the tube 200 or 20| when negative voltage is applied by way of either or both of these paths. During the A period, negative voltage is applied by way of the resistor |98 to the grid ci the tube 200, and during the B period, negative voltage is applied by way of the resistor |91 to the grid of the tube 20|. When PCM pulses are present in the A period, positive voltage is applied from the anode of the tube |85 to the grid of the tube 200. At the commencement of the following B period, positive voltage is applied to the same grid by way of the resistor |98 and this grid rises in potential, to fall again at the conclusion of this B period. By exactly similar action, the potential of the grid of the tube 20| rises at the termination of the B period, to fall again at the conclusion of the following A period. Thus the grids of the tubes 200 and 20| rise and fall in alternation. Since their anodes are connected in parallel, negative voltage remains applied to the output condenser 202 as'long as some one or more PCM pulses are present during each A period and each B period.

When, however, a gap in the train of PCM ypulses appears, enduring throughout a full sample period of seven pflse positions and representing a Start signal in the A period, then this alternation in the grid potentials of the tubes 200 and '20| is broken. As above explained, the upper single trip multivibrator fails to trip, and the anode of the tube |85 remains negative. At the conclusion of this blank A period, the cathode potential of the tube |14 rises. Now positive voltage is applied by way of the resistor 98 to the grid of the tube 200, but not by way of the varistor |95 so that the grid of the tube 209 remains negative. At this time the grid of the tube 20| is likewise negative. Thus the grids of both of the tubes 203 and 20| are negative, and a positive pulse 203 is transmitted by way of the condenser 202 to the Gates III. This is a Start pulse, coinciding with the duration of a B period and indicating the complete lack of PCM pulses,

` or the presence of a Start signal, in the preceding signal at that time, results in holding the poten-` Similarly, a totallack of PCM 16 tial of the gridV of the tube 20|` negative during the ensuing A period when the grid of the tube 209 isalso negative, and so in sending a Start pulse to the Gates III.

Each of the siX Gates I-II may be a time coincidence gate of any desired configuration, a suitable one being shown in Fig. 1 3. The start pulse 203 as derived by the Recognizer of Fig. 12 is applied,.simultaneously and in parallel, to all six of the Gates III, being applied in each case by way of a condenser 2|0 to the control grid of a pentode 2| while the pulses of the t2-2 train, derived from the second stage of the twelve-stage ring circuit |5| of Fig. 11, (the second segment of the commutator |5| of Fig. 10) are applied to its suppressor grid. Output pulses, which occur when the itz-2 pulse coincides with a start pulse, are negative at the anode of the pentode 2| and are then reinverted by a buffer amplifier 2|2 to furnish positive pulses by Way-of al'condenser 2 i3. These are applied in parallel and simultaneously to all fourteen of the Gates IV which are associated with channel No. 2. Similarly, the rst of the Gates III, which receives start pulses at its control grid and tz-I pulses at its suppressor, supplies all fourteen of the Gates IV which are associated with channel No. l, the third Gate III, which receives start pulses at its control grid and pulses of the 152-3 train at its suppressor, supplies all fourteen of the Gates IV which are associated with channel No. 3, and so on. Thus the function of the several Gates III is to sort the Start pulses as they arrive from the Recognizer in time division multiplex separation on a single conductor, into six groups associated with I 10,there are six for each listener or fourteen ior each channel, may be as shown in Fig. 14. Its pulse input point is the control grid of a triode 2|5 to which t2 pulses 4from the associated Gate III and t1 pulses from the odd-numbered stages of the twenty-eight stage ring |50 are applied together. Thus, assuming the Gate IV shown in detail invFig. 14 to be the one designated C-2 in Fig. l0, tl-C pulses are applied by way oi a condenser 2|9 and a resistor 2|1 to the grid of the tube, and similarly to the ve other Gates IV serving listener C, while the t2-2 pulses are applied by'way of a resistor 2|8 to the same grid and similarly to the 'thirteen other Gates IV served by channel No. 2. The anode of the tube 2 5 is directly connected to the anode of tube 22| F of a Inultivibrator. The tz-2 pulses are also applied by way of a condenser 223 and a resistor 224 to the grid of a tube 225, while the ti-C pulses are also applied to the grid of an inverter tube 225 and thence after inversion to the grid of the tube 225 by way of a condenser 221 and a resistor 228. The anode of the tube 225 is directly connected to the anode oi tube 222 of the multivibrator. 'Ihus, when a tz-E pulse from Gate III, signifying a Start signal, occurs within the period of a t1'-C pulse, the two are applied in like phase to the grid of the tube 2|5 and in opposite phase to the grid of the tube 225.

It is the function of Gate IV (C-Z) to establish a voice path from channel 2 to listener LC when the arrival of a Start signal in the proper time slot indicates that a message destined for listener C is about to commence on channel 2; and to disestablish this connection when a Start signal in any other time slot indicates that channel 2 is to Vbegassigned Ato.somesother listener. lReturning .to :consideration .of Eig. .11 and :.the original fincoming PCM pulses, after such regeneration ...and amplication as may be required, these are rst delayed by 10.4 microseconds by a suitable delay device 230 to compensate for the lag of 10.4 microseconds :introduced Lby the Recognizer, whereupon-theyl are supplied vto decoder apparatus 23| which 'recouvertsL themrom .theccoderrep resentation used in transmission.into-:voice signal samples. The lattervarefthen appliedLto a distributor 232 which routes -them intozztvvelve lines in rotationfof which the first sixsarerthose Iofthe upper .TASI system lof Fig .1= while=.the secondsix are those ofthe lower TASI'systemfof Fig. 1. "The K Voice signalfsamples .onfthe second'zlineearerapplied .to thefcontrol gridv of a tube3eof'flig. 14, Vtheanode of'Whichisconnectedby way ofsa condenser 236 to listener Csnstrument. ":Thusithe required Voice :path 1is .established from channel No.1.2 to listenerLCzbyuWay of-:.the .tube .235..When andfgonly when this tube fcon'ducts. '.Controlf'of its conduction yis .effected fby .the-'application :to itssuppressor. grid of the .voltage output-of ftube .1222-A of fthe multivibrator.

The manner: in4 Whichtt'he. apparatus ois-Fig. 14

operates-.to apply thegrequired voltage'nto-:the suppressor grid ,of-:thetube 23.5 :tosecurethe required result ...will be .described with respectto the `.condition. in .which Atalker .,A. is engaging .listener LA. by ,vs/,ayV of channel No.1, .channel No.f;6.is.si'milarly Aoccupied. by talker; B; and .listener LB,channelil-No. Zfhasrecently been occupied-by: some:.talker.=.other than.-A-B `and- C,;.and,.is fnow.;required.:by. talker ,Cfvvhowishes .toconverse Withlistener LC. ,Thus, prior .to thearrival of Y.the .C'-,2 StartfsglaLthe C-,r21GatelVfis in itsfinactive:.condition, therigbthandatube 222 `of themultivibrator isonducting itsanode potential is low,:and-.the voice gategtube 235, to .whose.suppressorfgrid-this potential is applied, is ,cut off. rlhe leftfhandtubej Lof the multivibrator.V is Vcutoff andiitsanode potential is high. Application; of this ,f potential to :the anode of :the tube1f2ii places thistubefinfreadiness to accept. incoming pulses. Thus, upon lthe time `listener puise,.the grid potentiaL-.of thetube 21H3 is raised to .thegpoint at -whicnvconduction takes place. The resulting pulseratf the sanode 10i' .the tube 2 |15 .is applied toitheggridoi' thefrignt-hand tube 222fand tripsAthegmultivibratorfto Vits.-.other condition of stability in winch-.fthe tube 222, is.r cut on', raising thek ,potential i, oi' -the suppressor grid of .the Atube n23:3 r.and establishlng y.the .required voice 4path .romfchannel -,No. v2 to .listener C. .At the same time the tube 22| becomes conducting andmits anode potentiali-alls. -Applicatlon of thls anode potentialv to the anode of tnetubeiimmunizes the tube 2te against operation bysubsequent zia-2 pulses and subsequent tl-C pulses, either oi' Whicnmay occur beorefthe lconclusion ortaiKer C's speech spurt.

This condit1onzholds-unti1 talker .CT-s speech spurt has been completedand .continues to-hold tnereaiter until a demandsis madeffor channel No. 2 by some other talker. When this occurs,

the appropriate Gate IV operates vas describedabove, and the C-Z Grate IV under` consideration is disabled by the` occurrence of aziz-2 start pulse which does not coincide Witha -ti-C pulse. In the absence of a ti-Cpulse, `the .t2-2;p11lse is appliedalone to the gridof thetube 2|5, butthis is of insuiiicient amplitude to cause conduction, and furthermore the tube has..been;disabled. as describedk above. @Theis-e2 rpulse is ;also applied lztof-thefzgrid vofthe tube..225. y.'I'he fit1-*C Wave,fn `.verted by the Ntube 2216, consists of .anegative `potentialduring.the pulse, '.Whichsthus prevents lconduction of 'the itube 2:25 .zwhenia start V,pulse r`coinciolesavvithsat1-C pulse, 'and of .apositive y potentialA atfall otherv times. '.When, 1.therefore,. a

.t2 start :pulseaarrives :which 'falls outsideof .the

:limitsy o'fsaLti-"C pulse, and Which-.therefore indicates'that zchann'el'. No. 2' is inf` demand-torsome :other listener, the :tube-'225 deliversia negative output pulse'fto thegridzof '.thei leftlhandrtube. 22| of'zthe;multivibrator' lWhich-drives thisstubeY below cut-off:andirestoresfthemultivibrator t0 its original condition of .readinessgalso interrupting the transmission path through tube 235.

:In `:a-Lbinary #permutation code system y for #the transmission ofvoicesignals such as the one with .Which-fthespresentv LTASIv system is combined, :the various #signal amplitude Values 1 may be J represented? by num-bers extending, in thefseven-dig'it code,1rom-OQOOOOOtoll11111. Insuch-.a system it tis `normal to bias fthe f-apparatus to the reenter of L"this irangef so =that l'the fformer symbol lrepre-- V.sente-*maximum ypeak-signal 'amplitudespf one sign fand the latter 1 represents :maximum signal vpeak 'amplitudesotheother sign. 'Off-all possible ramplitudes, :these :two occur `with the greatestr-ari-tylinthe course of anormal voicesignal. "-'12herefore.a,minimum of degradation of the signal-results'lvhen one of them uis selected as the Starts'ignal. IAS-between thesetwo there is no choice, vandiby-simple -modication Aof fthe Startsignal-'generator atbthe transmitter terminal `and fof ithe' Recognizer at '--the receiver terminal,

thef-otherfcouldr have beenfchosenfas-a 'Start'signal. Still other variations jof-the'Start signal, anclofffrthe generator-and Recognizer, v"as Well Yas Vo'ff'the-^circuit @detailsmf 'other=-apparatus components,-=are=poss"1ble.

What is claimedis:

` 1. In a 'speech transmission system,-aA terminal station, f a number o'fltransmitters at `said Station, a" lesser numberof communication channels `outgoing f'from said station, a'rst'funiformly rotating ='distributor Lfor-*oliering l-all 'of said channels in rotation-:toria Li-lrst vone of lsaid transmitters, va second uniformly rotating distributor -forfsubstituting all others of the transmitters, in rotation, for the first transmitter, talkspurt-operated means for establishing a connection from an active transmitter ato-.fan vidle channel at the instant .at which-such ichannel .is 'offered to such transmitten: and other .talkspurt-operatedimeans for removing-fa .-busy; channelffrom the Vgroup :of channels: oiered: to other transmitters during the vcontinuance ofia talkspurt.

.2. v1n ,a .speechsftransmission system, a terminal stationpa numberof.transmitters at said station, y

alesser number ofxcommunicationchannels outgoingiirom saidf'station, aiirst uniformlyrrotating .distributor for vvcollecting'speech energy-from all of :said transmitters.' in. rotation, 1a second :uniiormly .rotating-.distributor 'for supplying speech energyztogall :of-said channels .in rotation,.rcommon Ydriving Imeans `for :driving said.- distributors at -speeds rsuch that :all of said `channels are oiered in :rotation tto :each lof said transmitters in rotation,"talkspurt operated .means ior establishing a connectionfroman, active transmitter tofanidle channel `at the instantfat which such channel is offered to such transmitter, and :other talkspurt-operated means vfor removing -a busy channel 'from .the ygroup of-channels offered to other transmitters I during the continuance of va talkspult.

In a speech transmission system,'a terminal station, a number of transmitters at said station, a lesser` number of communication channels outgoing from said station, uniformly rotating means for offering all of said channels in rotation to each of said transmitters in rotation, talkspurt-- operated means for causing an active transmitter to which such offer is made to seize the first idle one of said channels, to hold it for speech transmission for the duration of a talkspurt and then to release it, talkspurt-operated means for preventing an inactive transmitter from seizing another line, and talkspurt-operated means for preventing the seizure of a busy line by any transmitter.

4. In a speech transmission system, a terminal station a number N of transmitters at said station, a lesser number M of lines outgoing from said station, a first distributor for collecting speech energy from all N of said transmitters in rotation, a second distributor for presenting all of said lines in rotation to each transmitter, voice-operated means connected to each transmitter, serving in'combination with said first distributor to identify a number n of active transmitters, up to but not exceeding M, and serving in combination with said second distributor to establish a connection from each active transmitter to an idle line, Avoice-operated means for preventing the seizure or" any busy line by a transmitter, means for sampling the messages in said M lines in rotation and for producing code pulse groups-representative of said samples, means for translating the location on the time scale at which an active transmitter seizes an idle line into a special code pulse group, means for combining said special code pulse group with said sample-representing code pulse groups, and means for transmitting all of said pulse groups to said second terminal.

5. In a communication system, a plurality N of incoming conductors, a lesser plurality M of outgoing conductors, means for distributing pulses of t1 duration among the incoming conductors in rotation, means for distributing pulses of t2 duration among the outgoing conductors in rotation, where a number MN of gates, of which M are associated with each incoming conductor, and N are associated with each outgoing conductor, each of said gates identifying one particular incoming conductor with one particular outgoing conductor, means for establishing a transmission path by Way of one of said/gates from one of said incoming lines to one of said outgoing lines, means for enabling each of said gates upon the temporal coincidence of the t1 pulse distributed to its incoming line, of the tz pulse distributed to its outgoing line, of activity in the incoming line and of inactivity in the outgoing line, means for generating a start pulse upon the joint occurrence of said four conditions, means for sampling signal energy appearing on said outgoing lines in rotation, means for translating each sample into a permutation code pulse group, means for transmitting said pulse groups in time sequence, and means for inserting said start pulse in said sequence.

6. In a communication terminal station, a plurality N of receivers, a lesser plurality M of incoming lines, a rst distributor for distributing pulses of t1 duration among the receivers in Multiplex basis. Y

rotation, a second distributor for distributing pulses of t2 duration among the lines in rotation, Where means for operating said distributors in syn-` chronism with similar apparatus at a transmitter terminal, means for translating incoming code groups of pulses into signal amplitude samples, means for distributing said samples among said lines in rotation, means for recognizing a code pulse group of a preassigned permutation code character as a start pulse, and means for establishing a voice path from an incoming line to a receiver upon the temporal coincidence of a t1 pulse distributed to said receiver, a t2 pulse distributed to said line, and a recognized start pulse.

7. In a speech transmission system, a rst terminal, a second terminal, a number N of transmitters at said rst terminal, an equal nurnber of receivers at said second terminal, a lesser number M of time division multiplex channels interconnecting said terminals, means at said rst terminal for assigning periods of t1 duration to said transmitters and periods of t2 duration to said channels, speechspurt operated means at said first terminal for establishing a communication path from an active transmitter` to an idle channel at an instant uniquely related to the t1 period assigned to said transmitter and to the t2 period assigned to said channel, synchronously operated means at said second terminal for assigning like t1 periods t0 said receivers and like t2 periods to said channels, means at said rst terminal for generating a start signal at an instant uniquely identifying a particular t1 period and a particular t2 period, and startsignal-operated means at said second terminal for establishing a communication path between a channel identified by said tz period and a receiver identified by said t1 period.

8. In a speech transmission system, a first terminal, a second terminal, a number N of transmitters at said-first terminal, an equal number of receivers at said second terminal, a lesser number M of time division multiplexed channels interconnecting said terminals, means at said first terminal for allotting idle channels to active transmitters in cyclic serial order and for generating a start signal each time such an allotment is made, and, at said second terminal, means controlled by said start signal for making like allotments of said channels to Vsaid receivers.

9. In a system for distributing a number M of speech signals originating in a greater number N of transmitters among a number M of transmission channels, the method whichcomprises examining all transmitters in rotation for activity, examining all channels, in rotation, for occupancy, applying a numberM of active transmitters to said channels in rotation at a rate equal to twice the highest message frequency, translating the message energy so applied to said channels into message code pulse groups, translating the location on the time scale at which a particular transmitter is applied kto a particular Ychannel into an identification code pulse group, and transmitting all of saidv code pulse groups to a receiver station on a Time Division 10. In a speech transmission system, a'transmitter terminal, a receiverterminal, two similar 'sets of Time Assignment Speech Interpolation Transmitter Apparatus at said transmitter terminal, each adapted to handle the calls originating in a number N of transmitters by Way of a lesser number M of channels, corresponding receiver apparatus at said receiver terminal, a time division multiplex transmissionk system of 2M channels interconnecting said terminals, and means at said transmitter terminal for supplying to said transmission system energy on each of the M channels of the rst set in rotation and for thereupon supplying to said transmission system energy on each of the M channels of the second set in rotation, whereby a full revolution of both sets constitutes a full revolution of the transmission system.

11. In a system for transmitting signals originating in a number N of transmitters to an l equal number of receivers by Way of a lesser number M of channels on a time division basis, a number N of transmitters, a iirst group of N conductors arranged in one direction, each coupled to a transmitter, a second group of M conductors arranged in a perpendicular direction, each coupled to a channel, said rst and second groups together dening a cross-net, a rst pulse distributor coupled to the transmitters, a speech detector coupled to each transmitter and to each conductor of the first group, a first group of gates one of which is coupled to each transmitter and to each conductor of the rst `group, each of said gates delivering an output signal only upon the simultaneous receipt of two input signals from different sources, each speech detector furnishing one such signal, when its transmitter is activated, to partially enable one of said gates, said distributor furnishing pulses to the gates of said rst group in sequence, said lastnamed pulses serving as the second-named input signals to said gates and so operating to complete the enablement of a gate of said first group which has been partially enabled by the signal furnished by the speech detector, a second group of gates, NM in number, one coupled to the first group conductor and to the second group conductor which denne each crosspoint of said net, each gate of said first group, when fully enabled, furnishing a signal to all M of the gates of the second group which are coupled to that conductor of the iii-st conductor group to which said last-named rst group gate is coupled, a second pulse distributor coupled to the channels and furnishing pulses to the several channel groups of the gates of the second group in rotation to complete the enablement of each second group gate Which has been partially enabled by a'rst group gate, each second group gate, when fully enabled, being operative to establish a speech path from that first group conductor to which it is coupled to that second group conductor to Whichiit is coupled, and to disable all other second group gates serving the same transmitter and all other second group gates serving the same channel.

12. In a speech transmission system, a terminal station, a iirst apparatus at said station comprising a iirst set of transmitters, N in number, a first set of outgoing lines, lVI in number, M being less than N, a rst distributor for collecting speech energy from all of said trans- 22 mitters in rotation, a second distributor for Sup-i plying speech energy to all of said lines in rotation, common driving means for driving said distributorsl at uniform speeds such that all of said lines are offered in rotation to each of said transmitters in rotation, talkspurt-operated means for establishing a connection from an active transmitter to an idle line at the instant at Which such line is offered to such transmitter, other talkspurt-operated means for removing a busy line from the group of channels ofered to other transmitters during the continuance of a talkspurt; and a second apparatus at said station comprising a second set of transmitters, N in number, a second set of outgoing lines, M in number, M being less than N, a third distributor for collecting speech energy from all of the transmitters of said second set, in rotation, a fourth distributor for supplying speech energy to all ofthe lines of said second set in rotation, common driving means for driving said third and fourth distributors at uniform speeds such that all of the lines of the second set are oiered in rotation to each of the transmitters of the second set in rotation, talkspurt-operated means for establishing a connection from an active second set transmitter to an idle second set line at the instant at which such line is oiered to Such transmitter, and other talkspurt-operated means for removing a busy second set line from the set of lines oiiered to other transmitters of the second set during the continuance of a talkspurt; a common time division multiplex transmission system of 2M channels coupled to the outgoing lines of said rst and second sets and operative in synohronism with said distributors, and means at said terminal station for supplying to said transmission system energy on each of the M lines of the first set in rotation and for thereupon supplying to said transmission system energy on each or" the M lines of the second set in rotation, whereby afull revolution of both sets constitutes a full revolution of the transmission system.

ALFRED E. MELI-IOSE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number 

